Sandpaper



Jam 19 1965 G. c. RIEGGER ETAI. 3,166,388

SANDPAPER Filed Jan. 2s, 1962 MQW 17mm/Er f United States Patent O 3,166,388 SANDPAPER l George C. Riegger, Miami Beach, Fla., and Richard M. Smith, New Brunswick, NJ., assignors to Johnson 8l Johnson, a corporation of New Jersey Filed Jan. 23, 1962, Ser. No. 169,704 9 Claims. (Cl. 51-296) The present invention relates to paper-backed abrasive papers, more particularly to such papers of the type known as sandpapers.

This application is a continuation-impart of my'copending application, Serial No. 829,629, led July 27, 1959, and now abandoned.

Conventionally, sandpapers have been made in the form of a laminate comprising a paper backing, a barrier material, and a layer of hard tough material having a layer of grits imbedded therein. The hard tough ma- A` ance when wet. v t l, The present invention vcontemplates a ,sandpaper in the' form of a laminate of the above general type, but which possesses superior internal strength, fold endurance, crack resistance, wet and dry tensile strength and` wet abrasion resistance.

Sandpapers according to this invention comprise a reinforced paper backing, a barrier material, a layer of making of a .barrier layer of iiex'ible material which only partly penetrates into one side of the-backing, or it may be 1in the form of flexible rubbery solids which penetrate `into and partially fill the voids in the paper backing throughout its thickness. When the term erubbery is used hereinafter in this application with reference toa materiaLi-t refers to the physical, not the chemical, properties thereof.'v In either case, the barrier material must `be (l) flexible, (2)

compatible with both the (a) paper backing and thefb) l f making varnish layer so as to bond toQ-both of tliem`,and (3) capable of preventing the making varnish tromperietrating substantiallyinto the backing.` i Y 'Ilhe backingis Va relatively heavy paperfn'or'mally hav- 3,166,388 Patented Jan. 19, 1965 ICC stices between the woodpulp fibers so that several of these interstices generally are located in each of the spaces between the reinforcing members.

The woodpulp `fibers are relatively small when com-i pared -with the reinforcing members, -i.e., the woodpulp fibers are in the range of about 0.04 to 0.4 mil in thickness and about 0.4 to 0.8 mil in width, and are less than 1A inch in length normally within the range of about S0 to 240 mils, while the reinforcing members are in the range of ,1 to mils in cross dimension and may be as long' as an inch or more, depending upon shape 'factors such as their length-to-width ratio. For instance, if they are in the form of rods having a more or less circular bers are in the form of granules, the cross dimension of the reinforcing members may be between about 5 and 35 mils.

In a given product according to this invention, the sizes of the reinforcing members and the woodpulp fibers are `of different orders of magnitude, i.e., the individual reinforcing members are at leastrabout 5, preferably 10 or more, times larger in cross-sectional area than the individual 'woodpulp fibers. Thus, even if equal proportions of the wood-pulp fibers and reinforcing members are used, the above-described relationship exists wherein the spaces between the reinforcing members are considerably vlarger than the interstices between the woodpulp fibers.

Y varnish and ailayer of abrasive grits imbedded in the making varnish. Thebarrier material may be in the form Y "ing a basis weight between about '40 and 150. `However,

lower basis weight backings may be advantageous in certain types Aof abrasive papersaccordingto this invention.`

When used in thisapplication, basis weight; shall be expressedrin pounds per ream of `480 sheets 24 incheswide" Howevter, it fvis animp'ortant advantagefof this invention and 36 inches long. Backings according to this inven-V `tion comprise a webor network of` overlapping crossing' kraft-type woodpulp fibers and a` multiplicity of hrelatively a large flexible and tough,thermoplastic"reinforcing members distributed substantially uniformlythroughout the' Webfin bonding relation with the woodpulp fibers. The Woodpulp fibers arearrangedin overlappingcrossing relation with one another so as'to define a multiplicity of minute interstices between them. t The relatively large Y reinforcing vr'nernoers definea corresponding multiplicity of Vspaces between the members the web. J'I'he averi age distance across the spacesjbetween the reinforcing members is considerably greaterfthanthe averagedis'tance across, or the sizeof, the relatively minute intersticeslbe.

tween the woodpulp fibers so that several-'of these inter- However, the reinforcing members are applied in the web `in certain definite proportionswhichgcontribute to the desited structure. j Normally, the, 0ver al1weight of the y 60'percent or more of the reinforcing members' by weight may be used `with desirable.V results forvcertain applications.

TheWoOdpulp'lfibers in the spacesfbetweeri the rein-5" Vforcing members .ini1the"'backings of` this invention are 'bonded to onefanotherby hydrationbonds formed between the fibers;V According to one embodiment ofthe invention, rubbery binder solids portions may be` present in the backing, J distributed substantially uniformly throughout the web ofwoodpulp libersto` .cooperate with the hydration bonds between the woodpulp fibers 'to bond the bers together. `Generally speaking, ,if the`amount off' 'rubberyr binder solids'in the backing is increased, trie`V internal strength ot the backing also, willbe increased.,

that backinigs may'be provided which when incorporated in 1 the above-described sandpaper'laminate provide an abrasive papen which' possesses superior Vinternal strength, i 'fold endurance, ycrack resistance, wetland :dry tensile strength andV wet abrasion resistance whether or not. the

rubbery binder solids,portionsare present. Therubbery binder solids. portionsl may betfapplied vto backings accrding tofthisinvention in different amounts depending" uponthe internal strength desired and cost considerations.

If cost is a prime factor, therubberyV binder solids may v p be dispensed with or `applied in relatively minor amounts.

However, when the making varnish, or grit bonding` layer, is a'rubbenlatex, for instance,1thej=rubbe'ry .binder solids may act as the barrier material ifpresentin the backing i in suicient amount, in which casesaid solids perform a double function, i.e. to increase Vthe internal strength ofV FIGURE 1 is an enlarged schematic View in elevation Y of a portion of an abrasive paper according to this invention;

FIGURE 2 is an enlarged schematic plan view of an abrasive paper according to this invention as one embodiment may appear; and

FIGURE 3 is a greatlyenlarged schematic sectional view of a portion of FIG. 1.

Referring to the drawings, there is shown an abrasive v paper comprising a reinforced paper backing e, a barrier layer 7, a layer 3 of making varnish and a multiplicity of grits 9 embedded in the making varnish layer 8. `ln the backing 6, relatively short and small woodpulp fibers lll are arranged in overlapping crossing relation with oneA another so as to form a multiplicity of interstices 12 between them. The woodpulp fibers are bonded together by hydration bonding between the fibers i1 where they cross yin contact with one another, aswell as by a multiplicity of relatively large rod-shaped flexible and tough thermoplastic polymeric reinforcing members 13 distrib-Y uted substantially uniformly throughout the web. i

Each of the reinforcing members 13 bonds a large number of woodpulp fibers ,11 which pass'through or,` into contact with the member. As shown most clearlyv in FIG. 3, the individualreinforcing members 13 entrap a number of adjacent or contiguous woodpulp tibersli in the plane of the Web and perpendicular thereto, orvthrough the thicknessof the web; The woodpulpfibers-lll are held firmly in:V the individual reinforcing members 13 since the Woodpulp fibers passing through eachV memberir are in contact'I with the materialof the reinforcing mem-, j ber-along a' high proportion of the length of the woodpulp fibers Vlli.

The reinforcing members 13 define ailmultiplicity.Y of

spacesg14` between,them;V and the average distance across the spacespisconsiderably greater than .the average dis# tance ,acrossA the interstices 12, .or the size of thelinterstices,j formed.l between interlacing woodpulp -fibersv1v1., Thus, vseveral of these interstices 12:-generally are located ineach'of the spaces 14 formed between the reinforcing members'l. t n

Inga sense, `the web is interruptedby the-reinforcing niembersll vso as toform aY multiplicity of.web islands corresponding tothe web ,arasf in the spaces ldbetween the reinforcingmembersj which are joined together by the reinforcing members. vContinuingthis analogy, the'j islands are formed byjthe woodpulp fibers 11 which are bonded together tojforrnv a connected network structurey Y in Jthe spacesllfThereinforcing members l3fdefiningf the islands may', be compared to hinges between islands which'` provide elements 'of flexibility scattered throughout 'the web structure. It is Ybelieved that the hingedy island structure .just described may'contribute to the improved flexibility of backings ,of this invention, although other factors such as fiber orientation'also may affect flexibility, t

In forming backings according to this invention, it isv preferredrto distribute, thereinforcing vmembers in the; web during the papermakinglstep'. Normally, thisystep involves beating the Woodpulp fibers to hydrate them to the extent necessary tofornr thedesiredhydration bonds-V f in thegbacking and .then distributingtthemY in water tol forman aqueous slurry of woodpulp fibers and mixing thev if proper proportion of thermoplastic reinforcing members with the woodpulp fibers in the slurry until they are distributed substantially uniformly in the slurry and intimately intermingled with the woodpulp fibers. The slurry is then drained through Some Sort of collecting means for making paper such as a Fourdrinier wire, a drum screen, a hand sheet mold, Or the like to form a paper Web. After drying and pressing as is conventional in papermaking, heat and pressure are applied to the web containing the reinforcing members in such a way as to soften and preferably fuse the thermoplastic reinforcing members and press them through the thickness of the 'Web so that they entrap a large number of woodpulp Vmade for this. Thus, the cross dimension of the reinforcing members in the resulting fabric may be as great as twice that of the rods or granules from which they are formed, although the increase in cross dimension due to the application of heat and pressure during the bond-' ing of the reinforcing members normally is not this great;

If it is desired to distribute rubbery binder solids portions in the backing, the Wood'pulp fibers need not be beaten prior to formation of the slurry orthey-may be beaten to some extent depending upon the properties desired in the finished product. After the bonds between the reinforcing members and the woodpulp fibers have been formed and the web has been allowed to cool to permit the bonds to become set, the rubbery binder solids i; may be applied thereto; Normally, this isaccomplished by impregnating thevweb with ari aqueous dispersion of a natural or synthetic rubbery latex, or byim'pregnating j it with a natural or synthetic rubber composition deposited from solution in` a volatile organic solvent` These meth.

ods are taughtin United States Patents 2,726,967 and t 2,236,527, respectively.

.Woodpulps,l the fibers.'l off which are v suitable 'for use inV producing backings in accordance with `this invention, in-

clude relatively long fiber kraft-type pulps,; such asDuracelY pulp.V As 4mentioned hereinbefore, theindividual woodpulp fibers arein'therange ofabout 0.04 to 0.4 mil in thickness and aboutQOA to 0.8 mil inzwidth, and generally are less than about .Mi inch, say about 80 to'240, mils, in

v length. From theabove, it is apparent thatrthe woodpulp' fibers are somewhat fiat, or ribbon.like,-in shape.

Theyrnay be4 more or less straightr or somewhat curled and kinked as mayv result from being subjected to treat vrnentsuch as'described in United States'Patentf 2,516,384

The relatively flexible and tough thermoplastic 't reinforcingL members ofthisinvention preferably are selected from among a number of long-chain polymeric materials Ywhich form fiexiblefand'tough ysolid granules or rods.

VNylon vcomprising polycaprolactam gives kparticularly good results when used as the material for the :reinforcing members of this invention. Other materials-,vwhich may be employed for the reinforcing members, includeknylon 11 such as sold under the 'trademark Rilsan2 by Organico, S.A., of France, Saran, polyamides other-'thannylons 6 and 11, polyvinyl chloride,V polyethylene, polyurethane,

polystyrene, polyvinylidene cyanide, plastici'zed cellulose acetate, plasticized ethylcellulose, and the like.Y v Y The sizeof the reinforcing members may-Vary over a widerange.' If the reinforcing'rmembers are in the shape of rods, prior to fusing, they normally would fall within the range of 'about' 6.5l1 00 denier, corresponding to about @OOM-0.004 inch in diameter prior to fusing for the flexible and tough thermoplastic materials of this invention, and (0,2 to 1 inch in length. Preferably, the rods would be between about and 60 denier, corresponding to about 0.001200034 inch in diameter prior to fusing, and in the neighborhood of 1A inch or less in length. If the reinforcing members of this invention are in the shape of granules, prior to fusing, they normally would be of such a size that 70 percent of the granules would not pass through a 200 mesh screen. Preferably, the majority of the particles are of a size that would not pass through a 100 mesh screen. This means that generally speaking the average granule size will be within the range of about 0.004-0.015 inch in diameter prior to fusing. Rods and granules outside the indicated ranges may be used provided that they are at least about 5, preferably 10 or more, times larger in cross-sectional area than the woodpulp fibers with which they are used.

The rubbery solids portions may be supplied from various natural and synthetic elastomeric materials, or mixtures of an elastomeric component with a thermosetting component, such as are described in United States Patents 2,848,105 and 2,848,355. As mentioned hereinbefore, the elastomer, or elastomeric mixture, may be in the form of an aqueous dispersion of a synthetic rubbery latex or a natural or synthetic rubber composition in solution in a volatile organic solvent. Suitable synthetic rubbery latices may comprise polymers of butadiene and other conjugated dienes and their homologues, and copolymers and tripolymers based thereon, vinyl chloride polymers, copolymers of vinyl chloride with other materials such as vinyl acetate and vinylidene chloride, chloroprene rubber and various other similarelastomeric polymers. Copolymers of butadiene and unsaturated nitriles, such as acrylonitrile and the like, have been found to be particularly suitable for this purpose.

Before application to the iibrous web, the rubbery binder solids may be in the form of relativelyV small particles ranging in size fromabout 0.004 to 0.2 mil in cross sec-l I between the woodpulp libers.` The rubbery binder material may remain in the form of the original relatively small latex particles in which it is deposited. However,l as the amount ofthe rubbery binder in the web is increased, the original latex particles tend to join one another and form an at least partiallyV continuous rubbery matrix with the rubbery binder solids lportions connecting the Woodpulp fibers' in` the Vareas 14 between the binder members 13 being in the form of agglomerates which mayV f be somewhat .film-like in character. `As the concentration of the rubbery binder solids portions is increased, the de# posited binder material becomes less particle-like and more like a continuous matrix in nature. 1

Abrasive papers according to this invention may be formed from the above-described `backings las follows. If

the rubbery binder solids are present in the web in suflicient amount (say about 10% by weight of theA dry fibers),

to act as a barrier material, the web" containing the rub! bery solids may be coated directly with a layer of-making varnish based on a rubberelatelx adapted to be vulcanized a In such a case the barrier material substantially prevents further penetration of the backingv in-situ on the web.

by the making varnish and is compatible with the backing and the making varnish layerso as to bond to both of them.

backing and is compatible with both the backing and the making varnish for bonding purposes. In this case, the main purpose of the barrier layer is to prevent the hard and tough making varnish from penetrating into the paper backing and rendering it hard and brittle. Various materials can be used for this purpose which are iiexible and capable of resisting penetration by the making varnish and capable of providing the required bonding between the varnish and the backing. The making varnish, itself, may be applied in two layers; the first being applied directly to the surface of the impregnated backing or the barrier layer, as the case may be, and the second being applied after the'grits have been seated in the first layer of making varnish. This` second layer sometimes is called the sandsize. As indicated above, the grits normally are applied in a layer tothe irst layer of making varnish while the varnish layer still is soft so that the grits are imbedded in the varnish as shown in FIG. 1 of the drawings. Conventional sand, or silicon carbide, grits or other abrasive grits of the type normally used in this general type of product may be employed. The sandsize is applied in a layer suiciently thick to assure that the grits will be held firmly in the making varnish afterthe varnish is dried, and the resulting product then may be dried and cured for several hours at an elevated temperature to bond the grits firmly in the varnish.

As indicated hereinbefore, the barrier material must be (l) flexible, (2) compatible with both (a) the paper backing and (b) the making varnish so as to bond to both of them, and (3) capableof preventing the making varnish from penetrating substantially into the backing. Diterent barrier materials accordingto this invention are listed below opposite typical making varnishes with which they may be used.

Barrier Material s Making Varnish 1 Oil compatible glyptal resln Resin from reaction product ot phenol aldehyde resin and fatty oil.

2 Halogenated rubber Halogenated rubber.

3.. vulcanized rubber vulcanized rubber.

4... Phenol-aldehyde resi Phenol-aldehyde resin.

5-.. do Urea-aldehyde resin.

6.-- Vinylracetal resin Phenol-aldehyde resin.

7 Ethyl cellulose resin Do.

8 Gelatim p-Plienol sulfonic acid rubber reaction product.

9 Plasticized polyvinyl chloride. Resin reaction product of melamine aldehyde resin and China-wood oil.

The `.following examples are illustrative of different Y embodiments of abrasive papers according to this invention.

l a i Example I a A sandpaper backing according to this invention is made fromcurlated Duracelpulp having a Schopper-Riegler freeness of about 750 cc.` and 20% by weightof the total mixture of 15 denier nylon 6 rods about JAG inch long. The above materials are collected on a-suitable papermaking screen toform a paper backing about 7.5 mils thick and Weighing about' 70 poundsjlpe'r ream. Bonds are formed between the nylon rodsandthe woodpulpbers bypre'ssing in a Carverfpress at 200 pounds per square i i-rich and 425 F. for 10 seconds;

When a hard and tough making varnish such as the resin reaction product of a melamine aldehyde `and China-wood oil is to be used, normallyrthe backing is coated with a tiex'ible barriermaterial such as polyvinyl Achloride lplasticized with a copolymer based on butadiene` 'which forms a layer on one side of the backing which will. prevent the making varnish from penetrating into the VThe backing paper is coated on one side with a barrier coat comprisingV polyvinyl chloride plasticized with aV copolymer of butadiene. and acrylonitrile (polyvinyl chloride to butadiene-acrylonitrile ratio being about 70:v `30) to deposit a barrier layer weighing about 6 pounds per ream. After drying, a coating of abrasive grainsis applied on top of the barrier coat by the following proctdure. About2.3V pounds per ream of a making varnish comprising the resin reaction` product of about20 parts l. of melamineformaldehyde resin and parts of a varnish based on China-wood oil is painted overthe barrier coat and aboutl4.5 pounds per ream of silicon carbide gritsra're applied thereto while the varnish still is wet. About 3,;8

pounds per ream of a sandsize of the same varnish is applied on top of the grits and then dried. The resulting product is cured for 8 hours at 225 F. This procedure is described more fully in Canadian Patent No. 568,647. The iinal curedl product is an inexpensive sandpaper of superior fold endurance, crack resistance, wet and dry tensile strength and wet abrasion resistance.

Example Il Another sandpaper backing according to this invention is made from curlated Duracel pulp having a Schopper- Riegler freeness of about 820 cc. and 15% by weight of the total mixture of 15 denier nylon 6 rods about 1/16 inch long in the same manner as for Example I to form a paper backing about 4 mils thick and weighing about 38 pounds per ream. This paper is treated as described in Example I to form bonds between the rods and the woodpulp fibers. The bonded paper is impregnated with a mixture consisting of about 99.5 parts on a solids basis of a butadieneacrylonitrile latex and about 0.5 part of the sodium salt of ethylene diamine tetraacetic acid in such a way that the total impregnant solids deposited weigh about 10% of the dry fibers in the sheet. The impregnated paper is then formed into a sandpaper laminate in the manner described in Example I to produce an inexpensive sandpaper which possessesisuperior fold endurance and crackresistance and exhibits internal strength, tensile strength and abrasion resistance when wet slightly greater than that of the paper of Example I on a weight-for-weight basis.

Example III A sandpaper backingis made and impregnated to deposit about 10% by weight of the dry fibers of rubbery binder solids, as described in Example II. The impregnated backing then is coated directly with about 7.5V

pounds per ream of a making varnish consisting of a vulcanizable rubber latex adapted to be heat curedI at au temperature or about 130 C. The rubbery binder solidsA in the web prevent the making Varnish from penetrating substantially into thebacking. While the making varnish' is stillwet about 4 pounds per ream of silicon carbide grits are applied thereto. The resulting product thenris cured for several hours at a temperature above 130'C.

to bond the grits lirmly in thevarnish. The resultingl productyis a liexible sandpaper of high crack resistance abrasive grits imbedded in said varnish, and a flexible barrier material preventing the making varnishjfrom pene.-v

trating Vsubstantially into'the backing, said barrier mate# rial beingcompatiblewith:'both the backing and the making varnish and'bondingthe. backing to the varnish, said web comprising a continuous networkV of kraft-type Wood` pulp fibers arranged in overlapping crossing relationship with one another so as to deiine a multiplicity of interstices between them, and a multiplicity of flexible and tough thermoplastic reinforcing members distributed substantially uniformly throughout the web in bonding relation with the Wood-pulp Vfibers, said reinforcing members being between about 1 and 35 mils in cross dimension and at least about ve times larger in cross-sectional area than said woodpulp bers and defining a multiplicity of spaces between said members, the average distance across the spaces between the reinforcing members being considerably greater than the average distance across the interstices between the woodpulp iibers whereby several of said interstices generally are located inreach of the spaces between the reinforcing members.

2. An abrasive paper according to claim 1, wherein elastomeric binder solids portions are distributed substantially uniformly throughout the web and said solids portions form a multiplicity of bonds between the woodpulp bers in theindividual spaces between the reinforcing members. i

3. An abrasive paper according to claim 1, wherein said thermoplastic,reinforcing members essentially comprise nylon. y

4. A711 abrasive paper according to claim 2, wherein said elastomeric binder solids also act as the barrier material and said making varnish comprises a vulcanizable rubber latex.

5. An abrasive paper according to claim 1, wherein said barrier material is inthe form of a flexible layer between said backing and the making varnish layer bonding the backing and thev making varnish to one'another, said barrier 'layer preventing substantial penetration of the making varnish into the backing.

6. An abrasive paper according to claim `1, wherein the Vreinforcing members are present kin the web in an amount ranging between about 5 and 30 percent based upon the combined dry weight of the fibers and the reinforcing members.

7. An abrasive paper according to claim 6,' wherein the reinforcedA backing web has a basis weight between about 40k and 150. I n y l Y 8.' An abrasive paper according to claim ,1, wherein Said reinforcing members are `rod-shaped.

9.* An`abrasive paper according to claim 8, wherein said rod-shaped reinforcing members are between about 1 and 5 mils in cross dimension.

nerereaes cata in the fue of this patent UNITED STATES PATENTS 

1. AN ABRASIVE PAPER WHICH COMPRISES A REINFORCED PAPER BACKING WEB, A LAYER OF GRIT SUPPORTING MAKING VARNISH ON ONE SIDE OF SAID PAPER WITH A MULIPLICITY OF ABRASIVE GRITS INBEDDED IN SAID VARNISH, AND A FLEXIBLE BARRIER MATERIAL PREVENTING THE MAKING VARNISH FROM PENETRATING SUBSTANTIALLY INTO THE BACKING, SAID BARRIER MATERIAL BEING COMPATIBLE WITH BOTH THE BACKING AND THE MAKING VARNISH AND BONDING THE BACKING TO THE VARNISH, SAID WEB COMPRISING A CONTINUOUS NETWORK OF KRAFT-TYPE WOODPULP FIBERS ARRANGED IN OVERLAPPING CROSSING RELATIONSHIP WITH ONE ANOTHER SO AS TO DEFINE A MULTIPLICITY OF INTERSTICES BETWEEN THEM, AND A MULTIPLICITY OF FLEXIBLE AND TOUGH THERMOPLASTIC REINFORCING MEMBERS DISTRIBUTED SUBSTANTIALLY UNIFORMLY THROUGHOUT THE WEB IN BONDING RELATION WITH THE WOOD-PULP FIBERS, SAID REINFORCING MEMBERS BEING BETWEEN ABOUT 1 AND 35 MILS IN CROSS DIMENSION AND AT LEAST ABOUT FIVE TIMES LARGER IN CROSS-SECTIONAL AREA THAN SAID WOODPULP FIBERS AND DEFINING A MULIPLICITY OF SPACES BETWEEN SAID MEMBERS, THE AVERAGE DISTANCE ACROSS THE SPACES BETWEEN THE REINFORCING MEMBERS BEING CONSIDERABLY GREATER THAN THE AVERAGE DISTANCE ACROSS THE INTERSTICES BETWEEN THE WOODPULP FIBERS WHEREBY SEVERAL OF SAID INTERSTICES GENERALLY ARE LOCATED IN EACH OF THE SPACES BETWEEN THE REINFORCING MEMBERS. 